It would be nice to have something in between listing and prepsrc.
Something that prints out the mnemonics and values and controls which lines are included as comments.

listing is amazing to see exactly how things get compiled because it gives the bytes rather than the mnemonics.

prepsrc however leaves as comments the (sometimes massive number of) macros used and more importantly it leaves all the conditional code, so to figure out which instructions actually got included in the final executable takes a lot of work.